Composite carbon fiber material and method of making same

ABSTRACT

A composite carbon fiber material is formed of one or more layers of carbon fiber material in which the carbon fibers are aligned all in the same direction and a mat of nonwoven, woven, or off-axis unidirectional carbon fibers are laminated together. Layers may be used individually or as a hybrid. The layers can be preimpregnated or impregnated during processing using thermoplastic or thermosetting resins. A layer of thermoplastic resin is applied either over the surface or within the composite structure, and the resin permeates the material so as to provide a more stable mechanical structure once the resin is processed. The material combines good mechanical strength with improved electrical current carrying properties when compared with the aligned carbon fiber layer alone. The layering sequence, layer type, and resin type can be specified to tailor electrical properties, mechanical properties, durability, and wear resistance. The resultant material achieves these results in substantially smaller material thickness than previously available.

This is a division of prior application Ser. No. 09/899,782 filed Jul.5, 2001, now U.S. Pat. No. 6,759,352.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a thin-gauge composite materialformed of layers of specialized carbon fibers and polymeric resins and,more particularly, to a composite carbon fiber material that is usefulin an electrical contact assembly typically used in an electromechanicaldevice.

2. Description of the Background

The use of carbon fiber material for structural applications is wellknown. Typically, this material is composed of multiple layers of eitherwoven fabric or layers of unidirectional, continuous carbon fibers thatare laminated together. The orientation and number of layers are chosento meet the stiffness, strength, and dimensional stability requirementsof the particular application. In typical aerospace applications thethin gauge material has between four to eight plies, with a thickness inthe range of 0.030 to 0.060 inches. Various processing methods forapplying heat and pressure to consolidate the layers of the carbon fiberreinforced thermoplastic and thermosetting composites include the use ofautoclaves, presses, and pultrusion. These carbon fiber materials can beformed or shaped by stamping, cutting and machining. The thermoplasticcomposites can be successively processed, for example, consolidation canbe followed by forming and welding. Although thin-gauge compositematerials exist, they are not suitable for microelectronic applicationspresently under consideration.

In U.S. patent application Ser. No. 09/498,872, assigned to the assigneeof this application and the disclosure of which is incorporated hereinby reference, it is proposed that an electrical contact be formed ofcarbon fibers that are arranged in a side by side fashion and embeddedin an electrically conductive matrix. Nevertheless, both the electricalcharacteristics and the mechanical characteristics of this carbon fiberelectrical contact are seen to be subject to improvement.

Therefore, the need arises for improvements in carbon fiber materials.

OBJECTS SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide animproved carbon fiber composite material that has similar mechanicalproperties as existing composites but with a smaller thickness, as wellas providing good electrical conductivity, and in which the material isa composite formed of carbon fiber materials and elastomeric resinlayers.

It is another object of the present invention to provide a compositecarbon fiber material having a layer of aligned carbon fibers that hasarranged on both flat sides thereof a nonwoven carbon fiber mat, wovenfabric or off-axis unidirectional layers with the outer surfaces of thecarbon fiber mats being finely coated with a polymeric resin.

A further object of the present invention is to provide a compositecarbon fiber material having multiple layers of the carbon fibers thatare aligned in a polymeric matrix and adhered together with the multiplelayers then being laminated with mats formed of nonwoven carbon fibers,woven fabric or off-axis unidirectional layers, with the exteriorsurfaces of the mats being coated with a polymeric resin for forming thecomposite material into a stable structure.

In accordance with one aspect of the present invention the carbon fibersthat are aligned and bound in a polymeric matrix are combined betweentwo nonwoven carbon fiber mats, woven fabric or off-axis unidirectionallayers. The nonwoven carbon fiber mats, woven fabric, or off-axisunidirectional layers provide improved mechanical strength and stabilityto the aligned carbon fiber layer and also provide a primary currentcarrying capability to aid in the overall electrical conductivity of thecomposite material. Unidirectional electrical conductivity can beachieved by using two methods: carbon fiber to carbon fiber contactbetween the individual layers that is applicable to both non-conductiveand conductive polymers; and/or by adding conductive materials to theresin layer or layers. The fabrication techniques utilized in making thecomposite material create a network of connections between thedifferently oriented carbon fibers to provide the desired electricalconductivity. The extent of this conductivity is regulated by the resinvolume fraction and may be increased by introducing conductive particlesinto the resin layer or layers of the composite.

The unidirectional carbon fiber layer is used for carrying electricalcurrent along a primary axis as well as creating mechanical stabilityalong that axis. Used alone, however, this material provides no off-axiselectrical conductivity and has virtually no off-axis mechanicalstability. The present invention teaches the use of a nonwoven fabric,woven fabric and off-axis unidirectional layer of carbon fibers toprovide off axis current carrying capabilities, as well as addingoff-axis mechanical stability.

The layer or layers of resin provide additional bonding material for theadditional carbon fiber layers and control the overall composition ofthe material. By varying the ratio of insulative resin to carbon fiber,the mechanical and electrical properties of the composite can betailored to meet a variety of applications. Also, by introducing andvarying the ratio of conductive particles to the resin layer or layersthe total electrical conductivity can be increased to be above thatwhich can be achieved by the network of carbon fibers alone.

The invention can contain one or more layers of each of theabove-described components depending on the desired electrical andmechanical properties specified and the material layering pattern may bechanged depending on the application requirements. By using the abovelayers of carbon fibers and elastomerics, the resulting compositematerial can be fabricated at a thickness of less than 0.010 inch.

The above and other objects, features and advantages of the presentinvention will become apparent from the following detailed descriptionof illustrative embodiments thereof to be read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view showing some of the various layers of thecomposite material relative to each other;

FIG. 2 is an end view of the inventive composite material showing all ofthe constituent layers thereof;

FIG. 3 is an exploded view of another embodiment of the materialaccording to the present invention in which two layers of aligned carbonfibers are arranged between two nonwoven carbon fiber mats;

FIG. 4 is an edge view of a composite material formed according to theembodiment of FIG. 3;

FIG. 5 is an exploded view of another embodiment of a composite materialaccording to the present invention in which there are two layers ofaligned carbon fibers in combination with three nonwoven carbon fibermats; and

FIG. 6 is an edge view of a completed composite material formedaccording to the embodiment of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 an exploded view of the inventive composite carbon fibermaterial is shown in which a central layer 20 is formed of alignedcarbon fibers that are held together by a plastic matrix. Arranged oneither side of the central layer 20 are mats 22 and 24 that are formedof nonwoven carbon. These mats 22, 24 are ultrathin carbon fibermaterial that is extremely light weight and uniform and is substantiallyisotropic, because there is almost no directionality of the fibers inthe plane of the nonwoven carbon fiber fabric.

As noted, the nonwoven carbon fiber mat is an ultrathin material and isgenerally available having a thickness from 0.08 mm to 0.79 mm. In thatregard, one commercial source for this nonwoven carbon fiber mat ormaterial is the Hollingsworth & Vose Company, 112 Washington Street,East Walpole, Mass. 02032.

The composite material is formed as shown in FIG. 2, in which followingthe arrangement of the mats 22, 24 over the aligned carbon fiber centrallayer 20 a thermoplastic resin or polymer is coated over the exteriorsurfaces of each mat. This forms layer 26 over mat 24 and layer 28 overmat 22. The thermoplastic resin layers 28 and 30 serve to bind or adherethe nonwoven carbon fiber mats 22, 24 to the respective outer surfacesof the central layer 20 formed of the aligned carbon fibers.

In another embodiment of the present invention, the central layer ofcarbon fibers is duplicated, however, the direction of the carbon fibersis changed so that the carbon fibers are at right angles to each otherin the successive central layers. More specifically, as shown in FIG. 3,a central layer of aligned carbon fibers 40 is provided and a secondcentral layer of aligned carbon fibers 42 is placed to be coextensivewith the first layer, however, in layer 42 the direction of thelongitudinal length of the carbon fibers is substantially perpendicularto the direction of the longitudinal length of the carbon fibers inlayer 40. The two layers 40 and 42 may be adhered to each other with asmall amount of thermoplastic resin. Thereafter a nonwoven carbon layer44 is arranged over the aligned carbon fiber layer 40 and a secondnonwoven carbon fiber mat 46 is arranged over the aligned carbon fiberlayer 42.

It is understood that the showing in FIG. 3 is an in-process assemblyand is not the final composite material, which in fact is shown in anedge view in FIG. 4. As seen in FIG. 4, a thermoplastic resin layer 48is applied over the nonwoven carbon fiber mat 44 and a similarthermoplastic resin layer 50 is applied over the nonwoven carbon fiberlayer 46. The effect of these thermoplastic resin layers 48, 50 is toform a stable material by causing adherence between each mat and itsrespective carbon fiber layer. Some of that same material, although notseen in FIG. 4 would also be applied between the respective carbon fiberlayers 40, 42 to bond those two layers to each other.

In another embodiment shown in FIG. 5, multiple layers of the alignedcarbon fibers are again provided. In this embodiment, both layers of thealigned carbon fiber structure have the fibers aligned in the samedirection. Specifically, a first carbon fiber layer 60 is provided and asecond carbon layer 62 is provided, however, a nonwoven carbon fiber mat64 is interposed between the two carbon fiber layers 60, 62. As in theprevious embodiment, a small amount of thermoplastic resin, not seen inFIG. 5, would be applied to both sides of the nonwoven carbon fiber mat64 in order to form a centrally arranged composite material. Thereafter,additional carbon fiber mats are provided on the outer surfaces of thecarbon fiber layers 60 and 62. More particularly, a nonwoven carbonfiber mat 66 is provided on an exterior surface of aligned carbon fiberlayer 60 and a second nonwoven carbon fiber mat 68 is provided on anexterior surface of the aligned carbon fiber layer 62, in which thefibers are aligned in the same direction as carbon fiber layer 60.

FIG. 6 shows the composite material finally assembled in the order ofthe layers as shown in FIG. 5, in which a thermoplastic resin layer 70is applied on the exterior surface of nonwoven carbon fiber mat 66 and athermoplastic resin layer 72 is applied on an exterior surface ofnonwoven carbon fiber mat 68.

One advantageous use for the above-described composite carbon fibermaterial is the manufacture of electrical contacts that conductelectricity and have a dynamic relationship to a resistive path.Therefore, the inventive composite carbon fiber material has been foundto provide improved current carrying capabilities because the nonwovencarbon fiber mats provide a primary current carrying capability and,moreover, the composite carbon fiber material has improved mechanicalstrength so that the resiliency required of such electrical contacts isimproved by use of this composite material.

It should be understood that, although not seen in the edge views ofFIGS. 2, 4, and 6, a small amount of the thermoplastic resin that formsthe exterior coatings of the composite material may also be appliedbetween the internal layers in order to make certain that all layers arefirmly bonded, one to another.

It is understood of course that the foregoing description is presentedby way of example only and is not intended to limit the spirit or scopeof the present invention, which is to be defined by the appended claims.

1. A method of making a composite carbon fiber material, comprising thesteps of: forming a central layer of a plurality of non-metallic carbonfibers aligned in a common direction and adhered to one another by anelectrically conductive resin matrix; arranging a first nonwoven carbonfiber mat in which the fibers are randomly arranged in the plane of thenonwoven carbon fiber mat on a first flat surface of the central layer;arranging a second nonwoven carbon fiber mat in which the fibers arerandomly arranged in the plane of the nonwoven carbon fiber mat on asecond flat surface of the central layer; coating an exterior surface ofthe first nonwoven carbon fiber mat with a layer of a thermoplasticresin; causing the thermoplastic resin to penetrate through the firstnonwoven carbon fiber mat to the first flat surface of the centrallayer; coating an exterior surface of the second nonwoven carbon fibermat with a layer of the thermoplastic resin; and causing thethermoplastic resin to penetrate through the second nonwoven carbonfiber mat to the second flat surface of the central layer.
 2. The methodof making a composite carbon fiber material according to claim 1,comprising the further step of: selecting the first nonwoven carbonfiber mat and the second nonwoven carbon fiber mat to have a thicknessin a range of 0.08 mm to 0.79 mm.
 3. The method of making a compositecarbon fiber material according to claim 1, wherein the step of forminga central layer comprises: forming a first layer of a plurality ofcarbon fibers aligned in a first common direction and adhered to oneanother by an electrically conductive resin matrix; forming a secondlayer of a plurality of carbon fibers aligned in a second direction andadhered to one another by an electrically conductive resin matrix,wherein the second direction is chosen to be substantially perpendicularto the first direction; and adhering the first layer to the second layerwith a thermoplastic resin.
 4. The method of making a composite carbonfiber material according to claim 3 comprising the further step ofarranging a third nonwoven carbon fiber mat between the first layer andthe second layer before adhering the first layer to the second layer.